Wireless data networks aim to provide users with guaranteed quality of service (QoS) levels while allowing network operators to exploit the statistical multiplexing gain associated with the fact that there are many users sharing multiple resources (i.e., the users not having those multiple resources solely dedicated to their individual requirements). This is in part due to the fact that the resource requirements of N multiplexed users, which may be bursty in nature, are less than the sum of the individual resource requirements for each user.
QoS guarantees require some kind of resource allocation. Following the conventional vocabulary, the period during which the resources, which are typically real circuits and switches, are allocated is referred to as a physical connection for a duration of a real circuit. When using statistical multiplexing, in contrast to the conventional vocabulary, the period during which the pool of shared resources are reserved is referred to as a "context" (i.e., logical connection) for a duration of a virtual circuit. In a wireless data network, this "context" begins with the activation of a packet data protocol virtual circuit (i.e., carrying packets from different external networks) and ends with the deactivation of the packet data protocol virtual circuit. This should not be confused with the fact that in a wireless data network there are both connection-oriented and connection-less services offered to applications. For instance, even if an application uses the internet protocol-type connection-less services of a wireless data network, there is a logical connection between the network layers in the mobile station and the base station. It is at this level that the admission control function operates. The admission control function of a wireless data network decides for each incoming virtual circuit request whether a sufficient aggregate pool of shared resources are available to satisfy the virtual circuit QoS requirements. The resources are dedicated to a particular virtual circuit only as they are actually needed to effect a data transfer and only for the duration of the transfer.
To perform resource allocation, the admission control function must be able to determine the load on each element of the network as well as its own network sub-systems. This includes but is not limited to any external network such as a packet data network, public switched telephone network, wireless data network, or neighboring public land mobile network, as well as its own network sub-system and base station sub-system. The admission control function is the central measurement consolidation and decision point for admitting new service requests to the network. This function could be placed at any node in the network such as the general packet radio service (GPRS) support node, the base station, the network management center or the mobile switching center to name a few.
In general, the load on a particular element of the network can be determined in two ways: (1) by looking at the accumulation of the previously granted service requests; and (2) by measuring the real load on the network. Measurement of the network load is usually performed by a network node such as a general support node or base station. Unfortunately, there are problems with determining the load on the networks, such as, responsiveness to load fluctuations and accuracy of accumulating service requests.
Measurement-based approaches particularly suffer from the following problem. With these methods there is a time delay during which the measurement must adjust to new traffic (i.e., service requests) that has been recently admitted to the network. During this period, the network can receive a new service request and grant this request believing that the wireless data network has enough surplus capacity to support the request. In fact, however, the wireless data network may not have enough surplus capacity because of the time delay associated with the measurement adapting to the previously admitted service request.
Admission control functions for the provision of the QoS have been investigated in Asynchronous Transfer Mode (ATM) networks. These ATM networks operate at very high speed (typically above 150 Mbps) and over reliable wired or optical fiber links. With such a high transmission speed, the admission control function can be non-optimal by being conservative in resource allocation and reserving more bandwidth than is minimally necessary to achieve the QoS. ATM networks normally carry a mixture of QoS classes including constant bit rate and variable bit rate with fixed delay. These classes are intended for use to transmit voice or video in which the delay is more important than the reliability of delivery (i.e., if the data is delayed then the data may be discarded rather than reliably delivering it). In contrast, wireless data networks have relatively low transmission speeds, typically below 200 Kbps, which must be highly optimized. In addition, data reliability is normally more important in wireless data networks than the delay. Robust transmission link methods such as forward error correction and automatic repeat request are necessary to achieve data integrity over the wireless data link which may be subjected to high levels of interference.
In conclusion, the existing admission control functions do not sufficiently satisfy the needs for efficient resource reservation in wireless data networks. Thus, there exists a need to improve the admission control function algorithms for networks in general, and in hybrid networks in particular, which may include wireless components which might exhibit limited bandwidth capacity or unreliability due to high levels of interference.